Some of Hollywood’s wealthiest stars are battling environmentalists over a $20million plan to save their houses on Malibu’s badly named Broad Beach. Steven Spielberg, Robert Redford, Dustin Hoffman, Goldie Hawn and Pierce Brosnan are among 108 homeowners along the 1.2-mile beach, where houses sell for up to $30million. When most of them were built in the 1970s, the owners had to walk 140 feet in the sand to reach the surf. Now, at high tide, the waves crash against an 8-foot-high emergency rock barrier. Though the stars want to spend their own money to rebuild the beach with sand dredged from the ocean floor, regulators have blocked the plan. Environmentalists prefer a “managed retreat” from the waves so the shore can revert to its natural state. Nancy Hastings of the Surfrider organization is sure the stars are committed to the environment, “But when your home is threatened, it puts things in a whole new perspective,” she told The Post’s Richard Johnson. Another eco-activist said, “They drive Priuses and have the right bumper stickers, but they care more about their houses.”